This invention relates to the field of ferrous metallurgy, specifically the blast-furnace process, and is applicable to feeding natural gas into blast furnaces.
In trying to reduce fuel consumption in a blast-furnace process by burning natural gas in a more efficient way, various gas regulation systems for blast furnaces have been developed.
One system was designed for regulation of the pressure and rate of natural gas injected into a blast furnace and for its distribution among the air tuyeres. That system consisted of: a natural gas supply pipe-line provided with a shutoff, safety, measuring and control instruments, a bypass line complete with gate valves and gas vent, and a circular manifold with connections for feeding gas to each air tuyere, the circular manifold provided with shutoff and safety devices. This gas regulation system suffers from a number of drawbacks. Among them are; lack of measuring and regulating devices in connecting pipes feeding natural gas to tuyeres, lack of devices preventing the formation of explosive mixtures in the gas regulation system, lack of a system for maintaining the prescribed ratio between the natural gas and blast air (or blast oxygen) flow rates, and lack of devices for preparation of natural gas for efficient combustion in the tuyere zone.
Another gas regulation system for use with a blast furnace, is the one consisting of the natural gas pipe-line with shutoff, safety, measuring and control instruments, a pipe-line, connected to the natural gas line and equipped with shutoff and control instruments, for purging and filling it with inert gas; a bypass line with shutoff and regulation instruments, and a distributing manifold with connections, equipped with shutoff, safety, measuring and regulating instruments, for feeding the gas to each air tuyere. This gas regulation system eliminates most of the drawbacks of the previous system but retains its main weakness, namely inability to prepare natural gas for efficient burning in a blast furnace which leads to excessive fuel usage in making pig iron.
The goal of the invention is to improve the last described process above to reduce the rate of fuel usage rate in the blast-furnace process.
In order to achieve this goal the present invention includes a gas regulation S system for a blast furnace consisting of natural gas and inert gas pipe-lines, a distributing manifold with gas supply lines to air tuyeres and a bypass pipe-line, as well as shutoff, safety, measuring and control instruments installed in those pipe-lines and a mixer in the natural gas pipe-line and an oxygen supply pipe connected to the mixer, with a by-pass pipe connected to the natural gas pipe-line before and after the mixer, and an inert gas pipe-line connected to the oxygen supply line.
Thus in one aspect the present invention is a system for introducing a mixture of natural gas and oxygen into the tuyeres of a blast furnace having a source of natural gas connected to a mixer via a natural gas supply pipe or conduit, the pipe having, upstream of the mixer, a flow control valve to initiate, control and terminate flow of a natural gas to the mixer, flow control means between the flow control valve and the mixer, with a check valve between the flow control means and the mixer, a source of oxygen connected to the mixer via an oxygen supply pipe or conduit the pipe having, upstream of the mixer a flow control valve to initiate, control and terminate flow of oxygen to the mixer, flow control means followed by a check valve between the flow control valve and the mixer, means to introduce an inert gas into the mixer, and means to by-pass the mixer to deliver natural gas, without mixing with oxygen and/or inert gas, directly to the blast furnace tuyeres.
In a preferred embodiment of the invention the mixer is made in the form of a cylindrical chamber with a diameter to length ratio being in the range of 0.4-0.7. A perforated tube, connected to the oxygen supply pipe-line with one end closed, is inserted into the cylindrical chamber with the longitudinal axis of the tube perpendicular to the longitudinal axis of the cylinder, wherein diameter of the perforated tube is equal to 0.15-0.5xc3x97 the diameter of the cylindrical chamber of the mixer. The total area of the holes in the perforated tube is in the range of 0.3-0.6xc3x97 the flow area of the tube with the diameter of holes in the range of 0.03-0.07xc3x97 the tube diameter.
FIG. 1 is a schematic representation of a gas regulation system according to the present invention.
FIG. 2 is a schematic representation of a mixer according to the invention.